Display substrate, manufacturing method thereof, and display device

ABSTRACT

A display substrate, a manufacturing method thereof, and a display device. The method includes: forming a pixel definition layer transitional pattern on a base substrate, the pixel definition layer transitional pattern being provided at a lateral surface with an undercut; forming a common layer, which is broken at the undercut, on the base substrate; removing the undercut to obtain a pattern of a pixel definition layer; and forming a cathode on the base substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.16/079,131 filed Aug. 23, 2018, which is the U.S. national phase of PCTApplication No. PCT/CN2018/074423 filed on Jan. 29, 2018, which claimspriority to Chinese Patent Application No. 201710449807.7 filed on Jun.14, 2017, which are incorporated herein by reference in theirentireties.

TECHNICAL FIELD

The present disclosure relates to a display substrate, a manufacturingmethod thereof and a display device.

BACKGROUND

Due to such advantages as self-luminescence, high brightness, wideviewing angle, high contrast, being flexible and low power consumption,an organic light-emitting diodes (OLED) display device, as anew-generation display device, has attracted more and more attentionsand has gradually replaced a conventional liquid crystal display device,which is widely used in mobile phone screens, computer displays andfull-color televisions. Different from a conventional liquid crystaldisplay technology, for an OLED display technology, it is unnecessary toprovide back light, and a very thin organic material layer and a verythin glass substrate may be adopted. When a current flows through theorganic material layer, the organic material layer may emit light. TheOLED display device has such many advantages, for example, being capableof achieving a flexible display. A flexible OLED panel may be achieved,if a flexible plastic substrate is adopted as a carrier, and a thin filmencapsulation process is adopted.

SUMMARY

Embodiments of the present disclosure provide the following technicalsolutions.

In one aspect, the present disclosure provides in some embodiments amethod for manufacturing a display substrate, which includes:

-   -   forming a pixel definition layer transitional pattern on a base        substrate, the pixel definition layer transitional pattern being        provided at a lateral surface with an undercut;    -   forming a common layer, that is broken at the undercut, on the        base substrate;    -   removing the undercut to obtain a pattern of a pixel definition        layer; and    -   forming a cathode on the base substrate.

Optionally, the removing the undercut to obtain the pattern of the pixeldefinition layer includes: heating the pixel definition layertransitional pattern to melt a part of the pixel definition layertransitional pattern, in such a manner to remove the undercut and form agentle slope, to obtain the pattern of the pixel definition layer.

Optionally, the forming the pixel definition layer transitional patternon the base substrate includes: forming at least two dam members on thebase substrate, which are located in a direction perpendicular to thebase substrate. The pixel definition layer transitional pattern includesthe at least two dam members, and the undercut is formed between two ofthe at least two dam members.

Optionally, the forming the at least two dam members on the basesubstrate includes: forming, on the base substrate, a first dam member,a second dam member arranged on the first dam member and a third dammember arranged on the second dam member. An orthogonal projection of atop surface of the second dam member onto the base substrate completelyfalls within an orthogonal projection of a bottom surface of the thirddam member onto the base substrate, and an edge of the orthogonalprojection of the top surface of the second dam member onto the basesubstrate is spaced apart by a certain distance from an edge of theorthogonal projection of the bottom surface of the third dam member ontothe base substrate.

Optionally, the forming, on the base substrate, the first dam member,the second dam member arranged on the first dam member and the third dammember arranged on the second dam member includes:

-   -   forming a first photosensitive material layer;    -   exposing a portion of the first photosensitive material layer        having a thickness d relative to an upper surface of the first        photosensitive material layer, to form an exposed film layer,        the first photosensitive material layer having a thickness D,        and D being larger than d;    -   forming a second photosensitive material layer on the exposed        first photosensitive material layer;    -   exposing portions of the first photosensitive material layer and        the second photosensitive material layer not shielded by a        light-shielding pattern of a mask plate, an orthogonal        projection of the light-shielding pattern onto the base        substrate overlapping an orthogonal projection of the pixel        definition layer onto the base substrate; and    -   developing the exposed first photosensitive material layer and        the exposed second photosensitive material layer to form the        first dam member, the second dam member and the third dam        member.

Optionally, the heating the pixel definition layer transitional patternto melt a part of the pixel definition layer transitional pattern, insuch a manner to remove the undercut and form a gentle slope includes:

-   -   heating the pixel definition layer transitional pattern to melt        a portion of the pixel definition layer transitional pattern, in        such a manner to enable lateral surfaces of the first dam        member, the second dam member and the third dam member to be        connected as the gentle slope.

Optionally, the thickness d of the exposed film layer is 1/10D to ⅕D.

Optionally, a thickness d1 of the second photosensitive material layeris ⅕D to ⅓D, and d1 is larger than d.

Optionally, the forming the at least two dam members on the basesubstrate includes forming, on the base substrate, the second dam memberand the third dam member arranged on the second dam member. Anorthogonal projection of a top surface of the second dam member onto thebase substrate completely falls within an orthogonal projection of abottom surface of the third dam member onto the base substrate, and anedge of the orthogonal projection of the top surface of the second dammember onto the base substrate is spaced apart by a certain distancefrom an edge of the orthogonal projection of the bottom surface of thethird dam member onto the base substrate.

Optionally, the forming, on the base substrate, the second dam memberand the third dam member arranged on the second dam member includes:

-   -   forming a first photosensitive material layer;    -   exposing the entire first photosensitive material layer;    -   forming a second photosensitive material layer on the exposed        first photosensitive material layer;    -   exposing portions of the first photosensitive material layer and        the second photosensitive material layer not shielded by a        light-shielding pattern of a mask plate, an orthogonal        projection of the light-shielding pattern onto the base        substrate overlapping an orthogonal projection of the pixel        definition layer onto the base substrate; and    -   developing the exposed first photosensitive material layer and        the exposed second photosensitive material layer to form the        second dam member and the third dam member.

Optionally, the heating the pixel definition layer transitional patternto melt a part of the pixel definition layer transitional pattern, insuch a manner to remove the undercut and form the gentle slope includes:

-   -   heating the pixel definition layer transitional pattern to melt        the portion of the pixel definition layer transitional pattern,        in such a manner to enable lateral surfaces of the second dam        member and the third dam member to be connected as the gentle        slope.

Optionally, the heating the pixel definition layer transitional patternincludes:

-   -   heating the pixel definition layer transitional pattern at a        temperature of 80° C. to 100° C. for 12 to 48 hours.

Optionally, the forming the common, that is broken at the undercut, onthe base substrate includes:

-   -   forming the common layer on the base substrate, where the common        layer includes a first common layer portion at a pixel region        defined by the pixel definition layer transitional pattern and a        second common layer portion at a top surface of the pixel        definition layer transitional pattern, and the first common        layer portion and the second common layer portion are        unconnected to each other.

Optionally, the forming the common layer on the base substrate includes:

-   -   forming a hole injection layer and a hole transport layer        sequentially on the base substrate, each of the hole injection        layer and the hole transport layer being broken at the undercut        at the lateral surface of the pixel definition layer        transitional pattern, one portion of each of the hole injection        layer and the hole transport layer being located at the pixel        region, the other portion being located at the top surface of        the pixel definition transitional pattern; and    -   forming an electron transport layer and an electron injection        layer sequentially, each of the electron transport layer and the        electron injection layer being broken at the undercut at the        lateral surface of the pixel definition layer transitional        pattern, one portion of each of the electron transport layer and        the electron injection layer being located at the pixel region,        the other portion being located at the top surface of the pixel        definition transitional pattern.

In another aspect, the present disclosure provides in some embodiments adisplay substrate manufactured through the above-mentioned method. Apattern of a pixel definition layer includes a first film layer and asecond film layer, and the first film layer is arranged at a side of thesecond film layer adjacent to a base substrate, and an etching rate ofthe first film layer is larger than an etching rate of the second filmlayer.

Optionally, the pattern of the pixel definition layer further includes athird film layer arranged at a side of the first film layer adjacent tothe base substrate, and an etching rate of the third film layer issmaller than the etching rate of the first film layer.

Optionally, a common layer is broken at a boundary between the firstfilm layer and the second film layer, and a cathode is continuous at theboundary between the first film layer and the second film layer.

In yet another aspect, the present disclosure provides in someembodiments a display device including the above-mentioned displaysubstrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the formation of an anode on abase substrate according to one embodiment of the present disclosure;

FIG. 2 is a schematic diagram showing the formation of a firstphotosensitive material layer on the base substrate according to oneembodiment of the present disclosure;

FIG. 3 is a schematic diagram showing a situation where the firstphotosensitive material layer is exposed according to one embodiment ofthe present disclosure;

FIG. 4 is a schematic diagram showing a situation where a secondphotosensitive material layer and the first photosensitive materiallayer are exposed according to one embodiment of the present disclosure;

FIG. 5 is a schematic diagram showing a situation where the firstphotosensitive material and the second photosensitive material layer aredeveloped according to one embodiment of the present disclosure;

FIG. 6 is a schematic diagram showing the formation of a hole injectionlayer and a hole transport layer according to one embodiment of thepresent disclosure;

FIG. 7 is a schematic diagram showing the formation of an electrontransport layer and an electron injection layer according to oneembodiment of the present disclosure;

FIG. 8 is a schematic diagram showing a situation where a pixeldefinition layer transitional pattern is heated according to oneembodiment of the present disclosure; and

FIG. 9 is a schematic diagram showing the formation of a cathodeaccording to one embodiment of the present disclosure.

DETAILED DESCRIPTION

In order to make the objects, the technical solutions and the advantagesof the present disclosure more apparent, the present disclosure will bedescribed hereinafter in detail in conjunction with the drawings andembodiments.

Inventors found in research that, for an OLED display substrate in therelated art, a common layer having a relatively large thickness isdeposited on a base substrate with a pattern of a pixel definitionlayer, and portions of the common layer at different pixel regions areconnected to each other. In this way, holes to be provided to eachsubpixel may probably be transported to an adjacent subpixel via thecommon layer. In this case, there is a leakage current between theadjacent subpixels, and thus light leakage may occur to an OLED displaydevice.

Embodiments of the present disclosure provide a display substrate, amanufacturing method thereof and a display device, so as to prevent theoccurrence of the leakage current between the adjacent subpixels,thereby to improve display quality of the display device.

The present disclosure provides in some embodiments a method formanufacturing a display substrate, including: forming a pixel definitionlayer transitional pattern on a base substrate, the pixel definitionlayer transitional pattern being provided at a lateral surface with anundercut; forming a common layer on the base substrate with the pixeldefinition layer transitional pattern; removing the undercut to obtain apattern of a pixel definition layer; and forming a cathode on the basesubstrate.

According to the embodiments of the present disclosure, the undercut isformed at the lateral surface of the pixel definition layer transitionalpattern. When the common layer is formed on the base substrate with thepixel definition layer transitional pattern, the common layer may bebroken at the lateral surface of the pixel definition layer transitionalpattern. In this case, one portion of the common layer is located at apixel region defined by the pixel definition layer transitional pattern,and the other portion of the common layer is located at a top surface ofthe pixel definition layer transitional pattern, so the portions of thecommon layer at different pixel regions are separated from each other.As a result, the holes to be provided to each subpixel are incapable ofbeing transported to an adjacent subpixel via the common layer, so as toprevent the occurrence of the leakage current between the adjacentsubpixels, thereby to improve a display effect of a display device.

A pixel definition layer in the display substrate manufactured accordingto the above method includes at least two layers, e.g., a first filmlayer and a second film layer laminated one on another. The first filmlayer is arranged at a side of the second film layer adjacent to thebase substrate, and an etching rate of the first film layer is largerthan an etching rate of the second film layer. In such a manner, whenthe pixel definition layer transitional pattern is formed throughetching during manufacturing the display substrate, the first film layeris indented inward relative to the second film layer, so as to form theundercut.

In some embodiments of the present disclosure, apart from the first filmlayer and the second film layer, the pixel definition layer may furtherinclude a third film layer arranged at a side of the first film layeradjacent to the base substrate, and an etching rate of the third filmlayer is smaller than the etching rate of the first film layer.

Optionally, the forming the pixel definition layer transitional patternincludes forming at least two dam members on the base substrate.

In some embodiments of the present disclosure, the forming the pixeldefinition layer transitional pattern includes:

forming a first photosensitive material layer; exposing a portion of thefirst photosensitive material layer so as to form an exposed layer;forming a second photosensitive material layer on the exposed firstphotosensitive material layer; exposing portions of the firstphotosensitive material layer and the second photosensitive materiallayer not shielded by a light-shielding pattern of a mask plate, anorthogonal projection of the light-shielding pattern onto the basesubstrate overlapping, e.g., falling within, an orthogonal projection ofthe pixel definition layer onto the base substrate; developing theexposed first photosensitive material layer and the exposed secondphotosensitive material layer, so as to form the pixel definition layertransitional pattern. The pixel definition layer transitional patternincludes a first dam member, a second dam member arranged on the firstdam member, and a third dam member arranged on the second dam member. Anorthogonal projection of a top surface of the second dam member onto thebase substrate completely falls within an orthogonal projection of abottom surface of the third dam member onto the base substrate, and anedge of the orthogonal projection of the top surface of the second dammember onto the base substrate is spaced apart by a certain distancefrom an edge of the orthogonal projection of the bottom surface of thethird dam member onto the base substrate.

In the above embodiments of the present disclosure, the pixel definitionlayer transitional pattern includes the first dam member, the second dammember arranged on the first dam member, and the third dam memberarranged on the second dam member. Of course, the pixel definition layertransitional pattern may merely include the second dam member and thethird dam member arranged on the second dam member. The orthogonalprojection of the top surface of the second dam member onto the basesubstrate completely falls within the orthogonal projection of thebottom surface of the third dam member onto the base substrate, and theedge of the orthogonal projection of the top surface of the second dammember onto the base substrate is spaced apart by a certain distancefrom the edge of the orthogonal projection of the bottom surface of thethird dam member onto the base substrate. In this way, when the firstphotosensitive material layer is exposed for the first time, the entirefirst photosensitive material layer, rather than a portion thereof, maybe exposed.

Because the undercut is formed at the lateral surface of the pixeldefinition layer transitional pattern, the subsequent formation of awhole layer of cathode may be adversely affected. Prior to the formationof the cathode, it is necessary to remove the undercut to obtain thepattern of the pixel definition layer. The removing the undercut toobtain the pattern of the pixel definition layer includes:

heating the pixel definition layer transitional pattern to melt a partof the pixel definition layer transitional pattern, in such a manner toenable lateral surfaces of the first dam member, the second dam memberand the third dam member to be connected as a gentle slope, thereby toobtain the pattern of the pixel definition layer.

In this way, when the cathode is formed on the substrate with thepattern of the pixel definition layer subsequently, it is able to formthe cathode with a continuous surface-like structure.

To be specific, the heating the pixel definition layer transitionalpattern includes:

-   -   heating the pixel definition layer transitional pattern at a        temperature of 80° C. to 100° C. for 12 to 48 hours.

In some embodiments of the present disclosure, the first photosensitivematerial layer has a thickness D, and a thickness d of the exposed layeris 1/10D to ⅕D.

In some embodiments of the present disclosure, a thickness d1 of thesecond photosensitive material layer is ⅕D to ⅓D, and d1 is greater thand.

In some embodiments of the present disclosure, the forming the pixeldefinition layer transitional pattern includes: forming the firstphotosensitive material layer; exposing the entire first photosensitivematerial layer; forming the second photosensitive material layer on theexposed first photosensitive material layer; exposing portions of thefirst photosensitive material layer and the second photosensitivematerial layer not shielded by the light-shielding pattern of the maskplate; and developing the exposed first photosensitive material layerand the exposed second photosensitive material layer, so as to form thepixel definition layer transitional pattern. The pixel definition layertransitional pattern includes a second dam member and a third dam memberarranged on the second dam member. An orthogonal projection of a topsurface of the second dam member onto the base substrate completelyfalls within an orthogonal projection of a bottom surface of the thirddam member onto the base substrate, and an edge of the orthogonalprojection of the top surface of the second dam member onto the basesubstrate is spaced apart by a certain distance from an edge of theorthogonal projection of the bottom surface of the third dam member ontothe base substrate.

In a possible embodiment of the present disclosure, the entire firstphotosensitive material layer is exposed for the first time.

Because the undercut is formed at the lateral surface of the pixeldefinition layer transitional pattern, the subsequent formation of awhole layer of cathode may be adversely affected. Prior to the formationof the cathode, it is necessary to remove the undercut, so as to obtainthe pattern of the pixel definition layer. The removing the undercut soas to obtain the pattern of the pixel definition layer includes heatingthe pixel definition layer transitional pattern to melt a part of thepixel definition layer transitional pattern, in such a manner to enablelateral surfaces of the second dam member and the third dam member toform a gentle slope, thereby to obtain the pattern of the pixeldefinition layer.

In this way, when the cathode is formed on the substrate with thepattern of the pixel definition layer subsequently, it is able to formthe cathode with a continuous surface-like structure.

In a possible embodiment of the present disclosure, the heating thepixel definition layer transitional pattern includes heating the pixeldefinition layer transitional pattern at a temperature of 80° C. to 100°C. for 12 to 48 hours.

In a possible embodiment of the present disclosure, the forming thecommon layer includes forming the common layer on the base substratewith the pixel definition layer transitional pattern. The common layeris broken at the lateral surface of the pixel definition layertransitional pattern in such a manner that one portion thereof islocated at a pixel region defined by the pixel definition layertransitional pattern and the other portion thereof is located at a topsurface of the pixel definition layer transitional pattern.

The common layer may include a hole transport layer and/or an electrontransport layer, and it may further include a hole injection layerand/or an electron injection layer. The common layer may be formedthrough evaporation or printing.

In a possible embodiment of the present disclosure, the forming thecommon layer includes: forming the hole injection layer and the holetransport layer sequentially on the base substrate, each of the holeinjection layer and the hole transport layer being broken at the lateralsurface of the pixel definition layer transitional pattern, one portionof each of the hole injection layer and the hole transport layer beinglocated at the pixel region, the other portion being located at the topsurface of the pixel definition transitional pattern; and forming theelectron transport layer and the electron injection layer sequentially,each of the electron transport layer and the electron injection layerbeing broken at the lateral surface of the pixel definition layertransitional pattern, one portion of each of the electron transportlayer and the electron injection layer being located at the pixelregion, the other portion being located at the top surface of the pixeldefinition transitional pattern.

The present disclosure further provides in some embodiments a displaysubstrate manufactured through the above-mentioned method. A pattern ofa pixel definition layer includes a first film layer and a second filmlayer, and the first film layer is arranged at a side of the second filmlayer adjacent to a base substrate, and an etching rate of the firstfilm layer is larger than an etching rate of the second film layer.

According to the embodiments of the present disclosure, the undercut isformed at the lateral surface of the pixel definition layer transitionalpattern. When the common layer is formed on the base substrate with thepixel definition layer transitional pattern, the common layer may bebroken at the lateral surface of the pixel definition layer transitionalpattern. At this time, one portion of the common layer is located at apixel region defined by the pixel definition layer transitional pattern,and the other portion of the common layer is located at a top surface ofthe pixel definition layer transitional pattern, so the portions of thecommon layer at different pixel regions are separated from each other.As a result, the holes to be provided to each subpixel are incapable ofbeing transported to an adjacent subpixel via the common layer, so as toprevent the occurrence of the leakage current between the adjacentsubpixels, thereby to improve display quality of a display device.

Optionally, the pattern of the pixel definition layer further includes athird film layer arranged at a side of the first film layer adjacent tothe base substrate, and an etching rate of the third film layer issmaller than the etching rate of the first film layer.

The present disclosure further provides in some embodiments a displaydevice including the above-mentioned display substrate. The displaydevice may be any product or member having a display function, e.g., anOLED panel, a television, a display, a digital photo frame, a mobilephone or a flat-panel computer. The display device may further include aflexible circuit board, a printed circuit board and a back plate.

The method for manufacturing the display substrate will be describedhereinafter in more details in conjunction with the drawings. The methodmay include the following step a to step i.

Step a: as shown in FIG. 1 , a thin film transistor array 2, aplanarization layer 3 and an anode 4 may be formed on a base substrate1.

The base substrate 1 may be a flexible or rigid substrate. The thin filmtransistor array 2 includes a plurality of driving thin film transistorscapable of driving organic light-emitting elements to emit light. Theanode 4 is connected to a drain electrode of each driving thin filmtransistor.

Step b: as shown in FIG. 2 , the first photosensitive material layer 5may be formed on the base substrate 1 acquired after step a.

To be specific, a layer of organic photosensitive resin may be coatedonto the base substrate 1 acquired after step a, so as to obtain thefirst photosensitive material layer 5.

Step c: as shown in FIG. 3 , the entire first photosensitive materiallayer 5 on the base substrate 1 may be exposed.

In this step, the entire first photosensitive material layer 5 on thebase substrate 1 may be exposed without any mask plate. During theexposure, an exposure dose may be controlled. For example, when thefirst photosensitive material layer 5 having a thickness D may beexposed completely at an exposure dose a, the exposure dose b adopted inthis step needs to be smaller than a, so as to merely expose a portionof the first photosensitive material layer having a thickness d.Preferably, d may be about 1/10D to ⅕D. After the exposure, as shown inFIG. 4 , an exposed layer 51 may be formed on the first photosensitivematerial layer 5, and a thickness of the exposed layer 51 may determinea size of the subsequently-formed undercut at the lateral surface of thepixel definition layer transitional pattern. When the thickness of theexposed layer 51 is too large, it is difficult to form the pattern ofthe pixel definition layer with a smooth lateral surface subsequently.When the thickness of the exposed layer 51 is too small, the undercut atthe lateral surface of the pixel definition layer transitional patternmay be of a too small size, and during the subsequent deposition of thecommon layer, the common layer may not be broken easily. Hence,preferably, the thickness of the exposed layer 51 may be 1/10D to ⅕D.

Step d: as shown in FIG. 4 , a second photosensitive material layer 6may be formed on the exposed first photosensitive material layer 5, andportions of the first photosensitive material layer 5 and the secondphotosensitive material layer 6 not shielded by a light-shieldingpattern of a mask plate 7 may be exposed.

To be specific, an organic photosensitive resin layer having a thicknessd1 may be coated onto the first photosensitive material layer 5, so asto form the second photosensitive material layer 6. Preferably, d1 maybe about ⅕D to ⅓D, and d1 may be larger than d. An entire arraysubstrate may be exposed through the mask plate 7. The mask plate 7includes the light-shielding pattern corresponding to the pattern of apixel definition layer and a transparent pattern. In this step, thefirst photosensitive material layer 5 and the second photosensitivematerial layer 6 may be completely exposed at a sufficient exposuredose, i.e., the entire first photosensitive material layer 5 also needsto be completely exposed.

Step e: as shown in FIG. 5 , the exposed first photosensitive materiallayer 5 and the exposed second photosensitive material layer 6 may bedeveloped, so as to form the pixel definition layer transitional pattern8. The pixel definition layer transitional layer 8 includes a first dammember 52, a second dam member 511 arranged on the first dam member 52and a third dam member 61 arranged on the second dam member 511. Anorthogonal projection of a top surface of the second dam member 511 ontothe base substrate 1 completely falls within an orthogonal projection ofa bottom surface of the third dam member 61 onto the base substrate 1,and an edge of the orthogonal projection of the top surface of thesecond dam member 511 onto the base substrate 1 is spaced apart by acertain distance from an edge of the orthogonal projection of the bottomsurface of the third dam member 61 onto the base substrate 1.

The pixel definition layer transitional pattern 8 may include: the firstdam member 52, the second dam member 511 arranged on the first dammember 52 and the third dam member 61 arranged on the second dam member511. The second dam member 511 may be exposed twice, so during thedevelopment, it may react with a development agent sufficiently. Afterthe development, the second dam member 511 may be indented inwardrelative to the first dam member 52 and the third dam member 61, so asto form the undercut. Due to the undercut formed by the second dammember 511, the lateral surface of the pixel definition layertransitional pattern 8 may be broken, as indicated by region A in FIG. 5.

Step f: as shown in FIG. 6 , a hole injection layer (HIL) and a holetransport layer (HTL) 9 may be formed on an upper surface of the entirearray substrate through evaporation.

Usually, each organic light-emitting element of an OLED display deviceincludes the hole injection layer, the hole transport layer, an organiclight-emitting layer, an electron transport layer (ETL) and an electroninjection layer (EIL) laminated one on another. Of course, one or moreof these layers may be omitted. The hole injection layer, the holetransport layer, the electron transport layer and the electron injectionlayer cover an anode of each subpixel and the pixel definition layer, soone or more of these layers may be defined as the common layer.

For ease of description, the hole injection layer and the hole transportlayer in FIG. 6 are combined as one layer, i.e., a layer 9. As shown inFIG. 6 , due to the undercut at the lateral surface of the pixeldefinition layer transitional pattern 8, the hole injection layer andthe hole transport layer may be broken at region A automatically duringthe deposition, so a portion of each of the hole injection layer and thehole transport layer on an upper portion of the pixel definition layertransitional pattern 8 may not be connected to the other portion on alower portion of the pixel definition layer transitional pattern 8, andthe portion of each of the hole injection layer and the hole transportlayer on the lower portion of the pixel definition layer transitionalpattern 8 may be located at a corresponding pixel region.

Step g: as shown in FIG. 7 , organic light-emitting material layers 10in various colors, e.g., red (R), blue (B) and green (G), may be formedat different pixel regions through evaporation, and the electrontransport layer and the electron injection layer may be formed on eachorganic light-emitting material layer 10 through evaporation. Theelectron transport layer and the electron injection layer are also partsof the common layer. As shown in FIG. 8 , the electron transport layerand the electron injection layer are combined as one layer, i.e., alayer 11. due to the undercut at the lateral surface of the pixeldefinition layer transitional pattern 8, the electron transport layerand the electron injection layer may be broken at region A automaticallyduring the deposition, so a portion of each of the electron transportlayer and the electron injection layer on an upper portion of the pixeldefinition layer transitional pattern 8 may not be connected to theother portion on a lower portion of the pixel definition layertransitional pattern 8, and the portion of each of the electrontransport layer and the electron injection layer on the lower portion ofthe pixel definition layer transitional pattern 8 may be located at acorresponding pixel region.

It can be seen that, the portions of the common layer at different pixelregions may be separated from each other, i.e., may not be connected toeach other.

Step h: as shown in FIG. 8 , the pixel definition layer transitionalpattern 8 and the common layer may be heated. At the region A, thesecond dam member 511 is indented inward, so the third dam member 61arranged on the second dam member 511 and the common layer on the thirddam member 61 may be suspended in the midair. During the heating, themelted third dam member 61 and the melted common layer may flowdownward, so as to remove the undercut at the lateral surface of thepixel definition layer transitional pattern 8, thereby to form thepattern 81 of the pixel definition layer with a gentle lateral surface.

The pixel definition layer transitional pattern 8 and the common layermay be heated under a specific condition, e.g., at a temperature of 80°C. to 100° C., or less, for 12 to 48 hours, especially at a temperatureof 95° C. for 24 hours. After the heating, as shown in FIG. 8 , theregion A may become a region B, and the pixel definition layertransitional pattern 8 may become the pattern 81 of the pixel definitionlayer with a smooth slope as the lateral surface. It should beappreciated that, although the lateral surface of the pattern 81 of thepixel definition layer is the smooth slope, through controlling theheating temperature and the heating time period, a portion of the commonlayer at a top surface of the pattern 81 of the pixel definition layermay not be connected to the portion of the common layer at the pixelregion.

Step i: as shown in FIG. 9 , a cathode 12 of the OLED display device maybe formed on an upper surface of the entire array substrate throughevaporation or any other process. As shown in FIG. 9 , after theheating, the lateral surface of the pattern 81 of the pixel definitionlayer is a continuous and gentle surface. Hence, the cathode 12 formedat the region B may not be broken like the common layer, and instead, itmay be of a continuous surface-like structure.

The OLED display substrate may be acquired through the above step a tostep i. It should be appreciated that, a type of the OLED displaysubstrate will not be particularly defined herein, i.e., the OLEDdisplay substrate may be of a top-emission or bottom-emission type.

According to the embodiments of the present disclosure, the undercut isformed at the lateral surface of the pixel definition layer transitionalpattern. When the common layer is formed on the base substrate with thepixel definition layer transitional pattern, the common layer may bebroken at the lateral surface of the pixel definition layer transitionalpattern. At this time, one portion of the common layer is located at apixel region defined by the pixel definition layer transitional pattern,and the other portion of the common layer is located at a top surface ofthe pixel definition layer transitional pattern, so the portions of thecommon layer at different pixel regions are separated from each other.As a result, the holes to be provided to each subpixel are incapable ofbeing transported to an adjacent subpixel via the common layer, so as toprevent the occurrence of the leakage current between the adjacentsubpixels, thereby to prevent the occurrence of such defects ascrosstalk and light leakage for the OLED display device as well asimprove the display effect of the display device.

Unless otherwise defined, any technical or scientific term used hereinshall have the common meaning understood by a person of ordinary skills.Such words as “first” and “second” used in the specification and claimsare merely used to differentiate different components rather than torepresent any order, number or importance. Similarly, such words as“one” or “one of” are merely used to represent the existence of at leastone member, rather than to limit the number thereof. Such words as“connect” or “connected to” may include electrical connection, direct orindirect, rather than to be limited to physical or mechanicalconnection. Such words as “on”, “under”, “left” and “right” are merelyused to represent relative position relationship, and when an absoluteposition of the object is changed, the relative position relationshipwill be changed too.

It should be appreciated that, in the case that such an element aslayer, film, region or substrate is arranged “on” or “under” anotherelement, it may be directly arranged “on” or “under” the other element,or an intermediate element may be arranged therebetween.

The above embodiments are preferred embodiments of the presentdisclosure. It should be noted that, a person skilled in the art maymake further improvements and modifications without departing from theprinciple of the present disclosure, and these improvements andmodifications shall also fall within the scope of the presentdisclosure.

What is claimed is:
 1. A display substrate, comprising a base substrateand a pixel definition layer arranged on the base substrate, wherein thepixel definition layer comprises a first film layer and a second filmlayer, the first film layer is arranged at a side of the second filmlayer adjacent to the base substrate, and an orthogonal projection of atop surface of the first film layer onto the base substrate completelyfalls within an orthogonal projection of a bottom surface of the secondfilm layer onto the base substrate, wherein the first film layercomprises a first dam member and a second dam member, the second dammember is arranged at a side of the first dam member away from the basesubstrate, wherein the second film layer comprises a third dam member,an orthogonal projection of a top surface of the second dam member ontothe base substrate completely falls within an orthogonal projection of abottom surface of the third dam member onto the base substrate, and anedge of the orthogonal projection of the top surface of the second dammember onto the base substrate is spaced apart by a certain distancefrom an edge of the orthogonal projection of the bottom surface of thethird dam member onto the base substrate.
 2. The display substrateaccording to claim 1, wherein an edge of the orthogonal projection ofthe top surface of the first film layer onto the base substrate isspaced apart by a certain distance from an edge of the orthogonalprojection of the bottom surface of the second film layer onto the basesubstrate.
 3. The display substrate according to claim 1, wherein anorthogonal projection of a top surface of the first dam member onto thebase substrate coincides an orthogonal projection of a bottom surface ofthe second dam member onto the base substrate.
 4. The display substrateaccording to claim 1, wherein an orthogonal projection of a bottomsurface of the second dam member onto the base substrate completelyfalls within an orthogonal projection of a top surface of the first dammember onto the base substrate.
 5. The display substrate according toclaim 1, wherein an orthogonal projection of a top surface of the seconddam member onto the base substrate completely falls within an orthogonalprojection of a top surface of the first dam member onto the basesubstrate.
 6. The display substrate according to claim 1, wherein thefirst dam member, the second dam member, the third dam member havedifferent patterns and/or thicknesses.
 7. The display substrateaccording to claim 1, further comprising a common layer that is brokenat a boundary between the first film layer and the second film layer. 8.The display substrate according to claim 6, wherein a sum of a thicknessof the first dam member and a thickness of the second dam member is D,the thickness of the first dam member is 1/10D to ⅕D, a thickness of thethird dam member is ⅕D to ⅓D.
 9. A display device comprising the displaysubstrate according to claim
 1. 10. A method for manufacturing a displaysubstrate, comprising: forming a pixel definition layer transitionalpattern on a base substrate, the pixel definition layer transitionalpattern being provided at a lateral surface with an undercut; andremoving the undercut to obtain a pattern of a pixel definition layer;wherein the forming the pixel definition layer transitional pattern onthe base substrate comprises: forming at least two dam members on thebase substrate, wherein the at least two dam members are located in adirection perpendicular to the base substrate, the pixel definitionlayer transitional pattern comprises the at least two dam members, andthe undercut is formed between two of the at least two dam members,wherein the forming the at least two dam members on the base substratecomprises: forming, on the base substrate, a first dam member, a seconddam member arranged on the first dam member and a third dam memberarranged on the second dam member, wherein an orthogonal projection of atop surface of the second dam member onto the base substrate completelyfalls within an orthogonal projection of a bottom surface of the thirddam member onto the base substrate, and an edge of the orthogonalprojection of the top surface of the second dam member onto the basesubstrate is spaced apart by a certain distance from an edge of theorthogonal projection of the bottom surface of the third dam member ontothe base substrate.
 11. The method according to claim 10, wherein theforming, on the base substrate, the first dam member, the second dammember arranged on the first dam member and the third dam memberarranged on the second dam member comprises: forming a firstphotosensitive material layer; exposing a portion of the firstphotosensitive material layer having a thickness d relative to an uppersurface of the first photosensitive material layer to form a fullyexposed film layer, the first photosensitive material layer having athickness D, and D being larger than d; forming a second photosensitivematerial layer on the exposed first photosensitive material layer;exposing portions of the first photosensitive material layer and thesecond photosensitive material layer not shielded by a light-shieldingpattern of a mask plate, an orthogonal projection of the light-shieldingpattern onto the base substrate overlapping an orthogonal projection ofthe pixel definition layer onto the base substrate; and developing theexposed first photosensitive material layer and the exposed secondphotosensitive material layer to form the first dam member, the seconddam member and the third dam member.
 12. The method according to claim11, wherein the thickness d of the fully exposed film layer is 1/10D to⅕D.
 13. The method according to claim 12, wherein a thickness d1 of thesecond photosensitive material layer is ⅕D to ⅓D, and d1 is larger thand.
 14. The method according to claim 10, wherein the forming, on thebase substrate, the second dam member and the third dam member arrangedon the second dam member comprises: forming a first photosensitivematerial layer; exposing the entire first photosensitive material layer;forming a second photosensitive material layer on the exposed firstphotosensitive material layer; exposing portions of the firstphotosensitive material layer and the second photosensitive materiallayer not shielded by a light-shielding pattern of a mask plate, anorthogonal projection of the light-shielding pattern onto the basesubstrate overlapping an orthogonal projection of the pixel definitionlayer onto the base substrate; and developing the exposed firstphotosensitive material layer and the exposed second photosensitivematerial layer to form the second dam member and the third dam member.15. The method according to 10, further comprising: forming the commonlayer, that is broken at the undercut, on the base substrate.
 16. Themethod according to claim 15, wherein the forming the common layer, thatis broken at the undercut, on the base substrate comprises: forming thecommon layer on the base substrate, wherein the common layer comprises afirst common layer portion at a pixel region defined by the pixeldefinition layer transitional pattern and a second common layer portionat a top surface of the pixel definition layer transitional pattern, andthe first common layer portion and the second common layer portion areunconnected to each other.
 17. The method according to claim 16, whereinthe forming the common layer on the base substrate comprises: forming ahole injection layer and a hole transport layer sequentially on the basesubstrate, each of the hole injection layer and the hole transport layerbeing broken at the undercut at the lateral surface of the pixeldefinition layer transitional pattern, one portion of each of the holeinjection layer and the hole transport layer being located at the pixelregion, the other portion being located at the top surface of the pixeldefinition transitional pattern; and forming an electron transport layerand an electron injection layer sequentially, each of the electrontransport layer and the electron injection layer being broken at theundercut at the lateral surface of the pixel definition layertransitional pattern, one portion of each of the electron transportlayer and the electron injection layer being located at the pixelregion, the other portion being located at the top surface of the pixeldefinition transitional pattern.
 18. The method according to claim 10,further comprising: forming a cathode on the base substrate.